For an animal with such a humble name, market squid have a spectacularly hypnotic appearance. Streaks and waves of color flicker and radiate across their skin. Other creatures may posses the ability to change color, but squid and their relatives are without equal when it comes to controlling their appearance and new research may illuminate how they do it.

Market squid skin changes color and pattern
Market squid skin is covered in chromatophores that expand and shrink to change the animal’s skin color or create camouflaging patterns ((Josh Cassidy/KQED))

Octopuses, cuttlefish and squid belong to a class of animals referred to as cephalopods. These animals, widely regarded as the most intelligent of the invertebrates, use their color change abilities for both concealment and communication. Their ability to hide is critical to their survival since, with the exception of the nautiluses, these squishy and often delicious animals live without the protection of protective external shells.

Cuttlefish and octopuses use closely packed chromatophores to match the color of their surroundings
Cuttlefish and octopuses use closely packed chromatophores to match the color of their surroundings (Josh Cassidy/KQED)

To actually control the color of their skin, cephalopods use tiny organs in their skin called chromatophores. Each tiny chromatophore is basically a sac filled with pigment. Minute muscles tug on the sac, spreading it wide and exposing the colored pigment to any light hitting the skin. When the muscles relax, the colored areas shrink back into tiny spots.

Tiny muscles expand chromatophores making the colored spots grow.
Tiny muscles expand chromatophores making the colored spots grow. (Josh Cassidy/KQED)

Because the system is based on the action of quick responding muscles, cephalopods are able to change colors almost instantly and can produce spectacularly intricate patterns to break up their outline.

Octopuses can mimic the color of stone
Day octopuses, like this one at California Academy of Sciences, can adjust their skin color, texture and body position to mimic a rock ((Josh Cassidy/KQED))

Hannah Rosen, a PhD candidate at Stanford University’s Hopkins Marine Station in Pacific Grove, is studying how exactly these animals control this dramatic light show. Squid are notoriously difficult to keep in captivity, so the first step toward studying them is to to head out into Monterey Bay to catch some specimens.

Rosen isn’t the only one fishing for squid. But while the squid aboard most of the fishing boats in the bay will end up served as calamari, the squid Rosen catches may help explain the mystery of how these creatures control their color change.

Market squid showing movement in once paralyzed chromatophores
After a few days, the chromatophores on this market squid’s left side began moving despite being disconnected from the brain’s signals ((Josh Cassidy/KQED))

Her research includes snipping a nerve that connects the brain to the chromatophores on one side of the squid’s body. When Rosen does this, the chromatophores on that side immediately relax and shrink to tiny spots, while the chromatophores on the intact side continue to flash normally. After a few days, some of the chromatophores on the paralyzed side began to move again, as if they were getting a signal from somewhere other than the squid’s brain. This phenomenon, Rosen says, is what fascinates her.

Rosen also tests how the fresh dead squid skin reacts to electric voltages when exposed to different pharmaceutical drugs in order to track down the neurological pathways involved.

By testing how they react to specific chemicals, Rosen hopes to discover exactly how squid control their chromatophores.
By testing how they react to specific chemicals, Rosen hopes to discover exactly how squid control their chromatophores. (Josh Cassidy/KQED)

While it’s still early to say, one possibility is that the skin itself is able to see and stimulate the chromatophores locally, bypassing the brain. A recent study at the Marine Biological Laboratory in Woods Hole, Mass., indicates that cuttlefish skin has light-sensing cells. Further investigation may help researchers understand how much of the color change control comes from the brain and how much is controlled by the skin itself.

For more info, you can visit:

California Academy of Sciences – Color of Life Exhibit
Monterey Bay Aquarium – Tentacles Exhibit

You’re Not Hallucinating. That’s Just Squid Skin. 27 September,2016Joshua Cassidy

Author

Joshua Cassidy

Joshua is a Digital Media Producer for KQED Science, and the Lead Producer and Cinematographer for Deep Look. After receiving his BS in Wildlife Biology from Ohio University, he went on to participate in marine mammal research for NOAA, USGS and the Intersea Foundation. He also served as the president of The Pacific Cetacean Group, a nonprofit organization dedicated to teaching students K-6 about whales. Josh studied science and natural history filmmaking at San Francisco State University and Montana State University.

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